Pneumatic tires are subject to failure from loss of air because of punctures, blowouts, or spontaneous leaks and then generally collapse. As a consequence, they are then likely to be severely damaged by rim cutting, or chafing, or breakage of cords, so that they are unsuitable for further use. Many efforts have been made to protect tires against such damage by use of auxiliary devices to prevent collapse. Such devices are expensive, cumbersome, and generally not completely successful.
It has now been found that with relatively small modification of structure pneumatic tires can be provided which will not collapse completely when inflation air is lost, and which therefore permit the user of a motor vehicle to continue to operate it without the need for changing tires at the roadside. Such tire constructions generally involve some kind of stiffening of the sidewall of the tire to minimize the amount of flexure which results from imposition of the weight of the vehicle on the tire in the absence of normal inflation pressure.
One form of such tires is described, for example, in the copending application for patent mentioned above. However, a requirement for successful performance of such a tire, both in the presence and absence of inflation air, is that the sidewall material, which undergoes the most severe deflection, be made of an elastomeric material having a high modulus of elasticity and a low hysteresis. Rubber compositions having this particular combination of properties have tended to change substantially during their service life so that a tire which could perform satisfactorily when new might not do so after it had been in use for some months or years.
The principal object of this invention, accordingly, is to provide a rubber composition of permanently high modulus and low hysteresis for use in the sidewalls of tires designed for operation both with and without inflation air.